Question

Procedure

1. Place the current balance assembly on a table opposite a wall or screen which is several meters away. Using the adjustable feet on the current balance, level the assembly. Make sure that the two conductors are as parallel as possible. A coin may be placed on the mass pan to hold the conductors together if adjustments of the lower conductor height are necessary. Adjust the counterpoise behind the mirror until the conductors are separated by an acceptable distance. A couple millimeter separation between the conductor edges is acceptable.

2. Position the laser such that it strikes the mirror and the beam is reflected onto the wall or screen. Note and mark the “equilibrium” position of the laser beam on the wall.

3. Connect the required circuit. The two conductors should be connected in series to the voltage supply. An ammeter arrangement must also be included in series so that the current may be accurately measured. Current must run in opposite directions through the wires. Make certain that the voltage is turned down to zero and then switch on the supply. As the voltage is raised slightly, the upper conductor should deflect upward and the laser beam spot on the wall should move. If this check does not work, something isn’t set up properly. 2

4. Using the fractional mass set, place 10 mg of mass on the pan. This amount of mass should not cause the bars to touch. If it does, increase the equilibrium separation distance between the conductors slightly. When adding mass to the bar you must be careful not to disturb the placement of the bar or else the equilibrium point may be changed.

5. Adjust the current until the beam spot is back to the equilibrium position. Measure and record this current to the nearest 1/100th of an amp. Note, if the current required for 10 mg on the pan is larger than 3 or 3.25 amps, the conductors are too far apart. Adjust the counterweight and remeasure until the current is low enough for 10 mg.

6. Repeat steps 4 and 5, increasing the total amount of mass on the pan by 10 mg. Determine and record the amount of current required to return the laser spot to the equilibrium position.

7. Continue to repeat steps 4 and 5 as often as possible until the required current will exceed the maximum you are not to surpass. Your instructor will tell you this value. You should be able to at least acquire data for total masses up to 90 mg.

8. Turn off the voltage supply and place a coin on the mass pan such that the upper conductor rests on the lower conductor. Measure and record the distance the beam spot has moved from the equilibrium point, D.

9. Measure and record the following distances: ℓ – the length of the two conductors which carried current, a – the distance between the conducting bar and the support knife-edge, and b – the distance from the mirror to the screen at which the laser spot was observed. Also measure the diameter of the conductors.

Questions:

1.. How could you modify the procedure such that you could repeat this experiment, resulting in data leading to the same graph, but have the current running through the conductors in the SAME direction?

2. An unknown current between 4and 6 amps is flowing through the conductors in opposite directions. Using the same setup you took data with, determine how accurately you would be able to determine the magnitude of this current. Justify with calculations and number.

Answer 1

Direction of force on the conductor depends on the direction of current flowing through it and direction of magnetic field. Direction of force is reversed when direction of current in conductor changes. So we want that current through the conductor to be in same direction , what we can do is we can use horse-shoe magnet near the conductor in the same procedure . So first adjust the poles of magnet such that it will create the magnetic field which will make the flow of current in opposite direction. After this , you can change the poles of magnet so that flow of current will also change , So using this method you will get same plot but direction of current will be same.This can be clearly understand using the flemings left hand rule. Force in the conductors will be repulsive if current flows in opposite direction and will be attractive when it flows in same direction.

B) we can calculate force and magnetic field through the current flowing and through the mean force you can calculate the accurate current using the formula

F= mu*l*(i)^2/(2*pi*d)

and F is known and I(current ) can be calculated by substituting others parameters